This invention relates to integrated circuits, and more particularly, to integrated circuits with memory element power supply circuitry that can be adjusted to supply overdrive voltages to selected circuit blocks on an integrated circuit.
Integrated circuits often contain memory elements such as random-access memory cells. Memory elements can be used to store data during digital processing operations. On programmable integrated circuits, memory elements can be used to store configuration data. Once loaded with a configuration data bit, a memory element can supply a static control signal to the gate of a programmable logic transistor. The logic high or logic low state of the configuration bit determines whether the transistor is turned on or off. By configuring numerous transistors, programmable logic on an integrated circuit can be programmed to perform a custom logic function.
The transistors that are configured in this way are typically formed using n-channel and p-channel metal-oxide-semiconductor transistor structures. When used to selectively pass or block the transmission of a data signal, these transistors are sometimes referred to as pass gates. Pass gates are often formed from n-channel transistors. When a low voltage is applied to the gate of an n-channel pass gate, the pass gate will be turned off and signals will be prevented from passing between its source and drain terminals. When a high voltage is applied to the gate of an n-channel pass gate, signals are allowed to pass between the source and drain terminals.
Due to the electrical properties of n-channel metal-oxide-semiconductor transistors, it is difficult to pass a logic one value between the source and drain terminals of an n-channel pass gate if the controlling voltage that is applied to the gate of the pass gate has the same magnitude as the logic one value. As a result, programmable integrated circuits are sometimes provided with memory elements that supply pass gate control signals at elevated voltages. These elevated voltages overdrive the pass gates when the pass gates are turned on and thereby improve pass gate performance.
The gate oxides of metal-oxide-semiconductor transistors can break down when subjected to excessively high overdrive voltages. Excessively high overdrive voltages should therefore be avoided to ensure adequate reliability.
While avoidance of high overdrive voltages can help improve reliability, overly conservative overdrive schemes can cause performance to suffer. If overdrive levels are inadequate, pass gates may be driven too weakly and may introduce unacceptable data path signal delays.
It would therefore be desirable to be able to address issues such as reliability and performance issues on integrated circuits with memory elements that produce overdrive pass gate control voltages.